This invention relates generally to injection molding and more particularly to valve gated apparatus wherein the valve member pistons have a spring in a spring chamber.
Valve gated injection molding systems or apparatus with pneumatic or hydraulic actuated pistons to reciprocate the valve member are well known. An example wherein the cap of the piston is retained in place by a resilient retaining ring is shown in U.S. Pat. No. 4,698,013 to Butcher which issued Oct. 6, 1987. However, the prior apparatus has the disadvantage that the components must be made to very precise tolerances with exact allowance for thermal expansion in order to have the front end of the valve member seated exactly in the gate in the forward closed position. If the front end of the valve member does not extend far enough forwardly to seat tightly in the gate in the closed position, an undesirable poor gate vestage will result. On the other hand, if the front end of the valve member extends too far forwardly, the repeated impact in the gate on closing will cause undue wearing of the front end of the valve member and the gate and can result in a fracture of the mold around the gate in some instances.